Various protein kinases are present in vivo, and are known to be involved in a wide range of functional regulations. RET is a receptor tyrosine kinase identified as one of the proto-oncogenes. RET binds to the glial cell line-derived neurotrophic factor (GDNF) and GDNF receptor to form a complex, which enables RET to perform physiological functions through intracellular phosphorylation signaling (Non-patent Literature 1). A study reports that in normal tissues, RET contributes to kidney development and neurogenesis during fetal life (Non-patent Literature 2). Some studies indicate that in cancers, such as lung cancer, thyroid cancer, breast cancer, pancreas cancer, and prostate cancer, the translocation, mutation, and overexpression of RET enhances its activation to thereby contribute to cell growth, tumor formation, or tissue infiltration (Non-patent Literature 3, 4, 5, 6, 7, and 8). In addition, RET is known to be a poor prognostic factor of cancer, as indicated in some reports that the translocation of RET and its enhanced activation level are also inversely correlated with prognosis in cancer (Non-patent Literature 9, 10, 11, and 12).
Therefore, an inhibitor capable of inhibiting RET activity is thought to be useful as a therapeutic agent for diseases associated with abnormally enhanced RET signaling pathways.
It is expected, for example, that in cancers involving translocated, mutated, and overexpressed RET, the administration of a medicament capable of specifically inhibiting RET will selectively and intensively suppress the proliferation of cancer cells and contribute to the treatment, life prolongation, and improvement in quality of life of cancer patients.
As such compounds having RET inhibitory activity, PP1 is known (Non-patent Literature 13). In PP1, a p-tolyl group is bonded to a fused ring pyrimidine skeleton. PP1 is known to exhibit high inhibitory activity against not only RET but also Src (Non-patent Literature 14), c-Kit, Bcr-Abl (Non-patent Literature 15 and 16), and others. For example, as side effects, the inhibition of Src may lead to abnormally enhanced bone formation, and the inhibition of Lck may suppress T cells (Non-patent Literature 17 and 18). Since multikinase inhibitors inhibit not only RET but also various signaling pathways to inhibit cell growth and other functions, the inhibitors raise concerns about possible various side effects, which may require dose reduction and/or drug holidays, thus leading to insufficient RET inhibitory activity. From the standpoint of side-effect reduction, RET inhibitors that have high inhibitory activity against RET with low inhibitory activity against other kinases have been desired.
Non-patent Literature 19 and Patent Literature 1 disclose a substance with a fused pyrimidine skeleton to which a ring structure is attached through an amide bond. This compound is described as having Aurora kinase inhibitory activity.
Patent Literature 2 discloses a pyrrolopyrimidine derivative that selectively inhibits Tie-2, TrkA, and its family member TrkB.
Patent Literature 3 discloses a pyrrolopyrimidine derivative that selectively inhibits Tie-2 and its family members.
Patent Literature 4 discloses a pyrrolopyrimidine derivative that is a potassium channel modulator.
Patent Literature 5 discloses a pyrrolopyrimidine derivative that has a therapeutic effect on diabetes.
Patent Literature 6 and 7 disclose a heterocyclic substituted cyclopentane compound that inhibits adenosine kinase.
Patent Literature 8 discloses a pyrrolopyrimidine derivative that has a vinyl group or an ethynyl group.
Patent Literature 9 discloses a fused pyrimidine derivative that has a BTK inhibitory activity.
However, none of Patent Literature above specifically discloses or even suggests an RET inhibitory compound with a fused pyrimidine skeleton that contains an amino group at the 4-position and a ring attached through an amide bond.